1. Field of the Invention
This invention relates to a developer detector that detects a developer in a hopper in an image forming apparatus such as a printer, a copier, or a facsimile machine employing an electrophotographic system, and a developing device including the developer detector.
2. Description of Related Art
Some image forming apparatus employing an electrophotographic system includes a hopper provided between a cartridge and a developer container. Some hopper includes a sensor that detects a developer (this sensor is hereinafter called a “developer sensor”). The developer sensor determines whether or not a developer is dropping while the developer is added from the cartridge to the hopper, or whether or nor the upper surface of the developer in the hopper has reached a height where the developer sensor is installed.
If an optical sensor is used as the developer sensor, the optical sensor can be housed in a sensor housing portion and can detect a developer through a detection surface formed of a transparent member. Such an optical sensor is installed near a transport region or a storage region for the developer, so that the developer is likely to adhere to the detection surface provided to the sensor housing portion. Thus, to prevent reduction in accuracy of detection by the optical sensor, the detection surface should be cleaned.
If the detection surface has a planar shape, the detection surface can be cleaned by making a flexible member slide on the detection surface while making the flexible member contact the detection surface under pressure. During the sliding motion, it is preferable that the flexible member be placed in a curved state according to which a front edge portion of the flexible member contacting the detection surface is positioned behind a base edge portion of the flexible member supported by a support member in a moving direction. This can stabilize the cleaning performance of the flexible member and the performance can be maintained at a high level, compared to a case where the flexible member slides on the detection surface in an inverse curved state of the aforementioned state. However, the flexible member may be in the curved state partially or entirely inverse of the preferable curved state when sliding on the detection surface. This makes it difficult to place the flexible member in the preferable curved state again while the flexible member remains contacting the detection surface under pressure. Not placing the flexible member in the preferable curved state again and leaving the flexible member as it is causes reduction in cleaning performance of the flexible member.
According to the configuration of a known developer detector, an interval between detection surfaces in a pair facing each other is set to be wider gradually in a position closer to an exit that is an end of passage of a flexible member (see Japanese published unexamined utility model application No. 6-16964 (1994), for example). In this conventional developer detector, as the flexible member moves, the degree of curvature of the flexible member is reduced gradually in a position closer to the exit.
Meanwhile, in the developer detector described in Japanese published unexamined utility model application No. 6-16964 (1994), the flexible member does not return instantaneously from a curved state. This makes it difficult to remove a lump of a developer adhering to the flexible member or a support member. The adhesion of the lump of the developer to the flexible member or the support member reduces the performance of the flexible member in cleaning the detection surface, leading to reduction in accuracy of detection by the optical sensor.
Additionally, in forming a configuration allowing removal of a developer from a flexible member or a support member, imposing limitation for example on an angle of arrangement of a sensor housing portion relative to a moving direction of a cleaning portion inevitably causes reduction in a degree of freedom in designing the sensor housing portion and other members.